Breathing devices for supplying oxygen to mine workers upon the occurrence of a catastrophic or incipiently disastrous event such as a cave-in releasing toxic gases or a fire depleting the atmospheric oxygen or filling the air with smoke particles are generally small light-weight masks detachably carried on a belt or a helmet. Such masks are capable of carrying only a severely limited oxygen supply and frequently are not sufficient for enabling escape from mines where exit passages are blocked or where poisonous fumes are extensive.
Breathing devices which have a sufficiently large store of oxygen are too heavy and bulky to permit their being constantly carried by mine workers or other personnel. These larger devices must then be temporarily stored, usually by the individual workers, at the mining site. A disadvantage of such a procedure lies in the fact that smoke and dust frequently become so dense as to block or at least seriously limit vision, thus inhibiting or preventing a timely application of the breathing devices. Such circumstances occasionally induce panic which only serves to increase the probability of casualty.